1. Field of the Invention
The present invention relates to clad plates and/or sheets with an excellent corrosion resistance property and a fabricating method thereof.
2. Description of the Background Art
Clad plates and/or sheets are composed of a clad metal and a substrate. For corrosion-resistant clad plates, the clad metal can be selected among the following materials due to their excellent corrosion resistance; stainless steels, Ni, Ni alloys, Co, Co alloys, Ti, Ti alloys, Ta, Ta alloys, Nb, Nb alloys, V, V alloys, Zr, and Zr alloys. The substrate can be selected among the Fe, Fe alloys, Cu, and Cu alloys which have enough mechanical properties for constructing a structure. The corrosion-resistant clad plates are used as a core material for heat exchangers, reaction vessels for chemical plants, ships, paper industries, constructions, bridges, pressure vessels, desalination and electric facilities, flue gas desulfurization plants, etc.
The clad plate consists of two layers of a clad metal/a substrate or three layers of a clad metal/an insert metal/a substrate, or more than three layers of a clad metal/insert metals/a substrate. The thickness of the clad metal is in the range of 5% and 50% of that of the substrate.
A basic function of the clad metal is to protect the substrate from the environment such as corrosion, chemicals, heat, wear, etc.
The insert metal layers takes a role of increasing the bonding strength between the clad metal and the substrate. The insert metal layers restrain a movement of elements such as Fe and C towards the clad metal from the substrate and prevent generation of the carbides and intermetallic compounds which make the interface between the clad metal and the substrate brittle.
The substrate should have enough mechanical properties to support the building structures.
The clad plates and sheets have been fabricated mainly by a roll bonding, an explosive welding, a spot welding, and a resistance seam welding. Among these methods, the resistance seam welding is known to be the cheapest method for fabricating the large-area clad plates and sheets. The explosive welding, the roll bonding, the spot welding, and the resistance seam welding have the following advantages and disadvantages.
The explosive welding: Since the substrate and the clad metal are bonded within a short time by an explosive energy of a gunpowder, the insert metal layer is not needed and the explosive welding method gives the most excellent bonding strength. However, a fabricating cost is expensive, a factory installation site is limited by a loud explosive noise generated at the time of the gunpowder explosion, and it is impossible to fabricate a large sheet and a thin sheet. Also, in case that the substrate is a thin plate, the substrate can be distorted by an explosive force of the gunpowder, thereby lowering ductility.
The roll bonding: The roll bonding, which bonds the substrate and the clad metal using a rolling mill, can fabricate the large clad plates and sheets cheaply. However, it requires an expensive installation cost (the rolling mill and a vacuum furnace). Also, since the bonding is performed at a high temperature, the brittle carbides and intermetallic compounds can be easily generated at the interface between the base metal and the clad metal.
The spot welding: Since the spot welding has to be performed many times in order to fabricate the clad plates and sheets having an excellent bonding strength, much time is required to the bonding, a bonding strength is low, and a complete sealing between the clad metal and the substrate is difficult.
The resistance seam welding: Since the substrate and the clad metal are placed between two electrodes and then an electric current and a pressure are simultaneously applied to the electrodes to bond the substrate and the clad metal within a short time, a bonding portion is scarcely oxidized. Also, the large clad plates and sheets of a circle shape and a straight line shape having an excellent bonding strength can be fabricated, and an installation cost and a fabricating cost are the cheapest.
In Japanese Showa Entetsu, the clad plates and sheets having a structure of the clad metal/the insert metal (net/thin sheet)/the substrate is fabricated by the resistance seam welding and used as a raw material of a heat exchanger, a chemical plant, and a flue gas desulfurization lining. In case that the clad plates and sheets for corrosion resistance is fabricated by a method developed in the Japanese Showa Entetsu, the metal net is stuck into the clad metal, so that the thickness of clad metal layer becomes thinner and the bonding strength between the clad metal and the substrate is lowered due to incomplete bonding.
On the other hand, in Korean Jungwon engineering company, C276/steel clad plates and sheets having an excellent bonding strength (300xcx9c360 MPa) are being produced by the resistance seam welding. The C276/steel clad plates and sheets are being used as a raw material of a flue gas desulfurization chimney lining. Recently, Jungwon developed the technique based on the resistance seam welding is for manufacturing Ti/steel clad plates and sheets. However, the interface between Ti and steel was uneven and the bonding strength was 200 MPa, lower than that of the C276/steel clad plates and sheets. Such a low bonding strength can result in the separation of the Ti clad metal and the steel substrate when the Ti/steel clad plates are used in a real plant. Accordingly, in order to commercialize the corrosion-resistant clad plates and sheets which are composed of the corrosion-resistant clad metal (Ni alloys, Co alloys, Ti, Ta, Nb, V, Zr, etc.) and the substrate (Fe, Fe alloys, Cu, Cu alloys), the interface bonding has to be excellent and a fabricating technique for the clad plates and sheets having an excellent bonding strength is required.
In the conventional method for fabricating the clad plates and sheets, the insert metal layer is inserted between the clad metal and the substrate and then at high temperatures heat or heat/pressure is applied, so that the different metals are bonded by a solid state diffusion reaction between the clad metal and the insert metal layer or the insert metal layer and the substrate. Accordingly, in case of fabricating the clad plates and sheets by bonding the clad metal which is not easily bonded like Ti to the different substrate metal, the bonding is insufficient and the bonding strength is low. Especially, in the resistance seam method, the clad metal sheet to be bonded and an electrode have to be contacted within a short time and bonded within a short time by the solid state diffusion, thereby having a problem in bonding completely. Also, in order to use the clad plates and sheets widely, the bonding strength has to be excellent and a cost of the clad plates and sheets has to be cheap.
Therefore, an objective of the present invention is to provide clad plates and sheets having an excellent bonding strength between the clad metal and the substrate.
Another objective of the present invention is to provide a fabricating method of the clad plates and sheets by which a bonding is performed within a short time and a fabricating cost is reduced.
Still another objective of the present invention is to provide the clad plates and sheets for corrosion resistance having an excellent bonding strength by a resistance seam welding, in which another metal having an eutectic reaction with the clad metal is inserted as an insert metal layer with one layer or multi-layers between the clad metal and the substrate and then an electric current and a pressure are simultaneously applied.
The foregoing and other objectives, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.